When you know the direction of sought potential but don't know by how much you need to alter somethign go for a half way solution. it will never be perfect but also never worse than before.

In case of ellipical wing ends. This is mathematically a sound way to go however in practical sense we don't see mnay of them. Even at the time of is invention greatest use (Spitfire airplane and era) the competition didn't copy it. The mustang I believe just had a trapezium like section at the end of its wing that could be regarded as a rough approximation of the elliptical wing.

One thing that strikes my most is that C-class fixed wings don't use elliptical tips (anymore). They all use a trapezium section on top of a rectangular section. I even believe that the the straight top is between 35 and 55 % of the foot of the sections.

So for your daggerboards I would not go with ellipical but with a trapezium section on the bottom 33 % of the wetted length with an end tip that is 50 % of the greatest width.

I suspect that this will get you close enough to lower drag while keeping sufficient area in the board when satisfying the class limits. I would also keep the trailing edge straight, you don't want a vertical vortex developping on your trailing egde. But it must be said that opinions differ about that. Some keep the leading egde straight and put the trapezium on the back.

Move your greatest thickness back as suggested by that monohull article. I know that several other board builders have done this as well. I seems to work for them. Somewhere between 30 % and 50 %. When able let the thickness reduce proportionally with the width of the board. Don't make the trapezium while maintain the full width of the board. That won't work well.


Make sure that your leading edge is a parabolic section. This is a compromise for good behaviour at both low and high speeds. A blunter parabola will give greatest steering force at low speed by ventilated earlier and give higher forces before venting at higher speeds. A sharp leading edge (a sharp parabola fairing) will have slightly less lift with a little more drag than the optimal parabola leading edge section when at low speed. At high speeds it will vent at 80 % of the maximum force attainable but flow will still reattach quickly when rotation is reduces. What ever you do do not use circular leading edges At has all the characteristics of a sharp leading edge but with the disadvantage that flow is reluctant to reattach. Bets compromise : 9-10 % thick section with with a small leading egde radius followed by a parabola over the forward 15 % of the cord. The higher the speed the finer the leadin edge must be. 18 foot skiffs mid wind range boards use radii of 0.5 %(source Bethwaite High Performance sailing)

Polish and buff your board and make them absolutely spotless and smooth the difference between smooth and buffed to a mirror can be 25 % addition force. Especially for rudderblade this is desired.

make the trailing edge sharper than the leading edge but you can get away with having almost a symmetrical crossection shape that is a little bit skewed towards the front Max thickness at 45 % or so.

Concave sections in the last 30% ; I don't know much about these. They seem to help prevent humming I'm told, but then again teh guy wasn't really an expert.

And buy Bethwaites book !

Good luck